Methods of preventing, controlling, and removing alluvium in cooling water systems



United States Patent 3,288,640 METHODS OF PREVENTING, CONTROLLING, AND REMOVING ALLUVIUM IN COOLING WATER SYSTEMS Howard G. Flock, Bethel Park, Pa., assignor to Calgon Corporation, a corporation of Pennsylvania No Drawing. Filed Jan. 11, 1965, Ser. No. 424,816 Claims. (Cl. 134-22) This invention relates to methods of preventing, controlling, and removing deposits of alluvium in cooling water systems and ballast tanks through the use of certain polyimines.

Much of the water used in industrial cooling water systems is obtained from rivers, ponds, lakes, or like sources and contains various amounts of silt, clay, mud, organic wastes, or low solubility salts which deposit on the surfaces of the system as alluvium. Moreover, in systems where cooling water is passed through cooling towers and then recirculated, airborne solids may become entrained in the water in its passage through the tower, and subsequently deposited in the system in a manner similar to natural alluvium. These alluvial deposits facilitate or cause corrosion, prevent the efi'icient transfer of heat, and reduce the capacities of passageways.

Because of alluvial deposits, entire water systems must be periodically closed down and cleaned mechanically, with acid, or by some other means. This may mean not only that the water system is closed down but also that systems depending on the water system must be closed down. Such a cleaning operation can be very costly. Furthermore, since such cleaning can only be performed at relatively infrequent intervals, it is not possible to maintain the heat exchange efficiency of the system continuously at a high level.

I have discovered a method of preventing, controlling, and removing alluvial deposits which does not require a lengthy shutdown of the water system, and makes out-ofservice cleaning operations far less frequent or entirely unnecessary. A method of my invention comprises periodically adding to the water in the system or continuously maintaining in the water a small amount of a watersoluble polymer polymerized from monomers of the general formula where R is H or an alkyl group having up to 4 carbon atoms, and R is R, or a hydroxyalkyl group having up to 4 carbon atoms. These polymers should have molecular weights of at least about 1000, although I prefer a molecular weight of at least about 50,000. Higher molecular weight polymers are preferable, as they are generally more effective.

While I do not wish to be bound by any theories, it appears that the compounds of my invention remove alluvial deposits from surfaces by dispersing the deposits into the water stream and agglomerating the deposits into a mobile fioc which can be carried away from the surfaces by the water stream. Several laboratory experiments described herein illustrate this dispersing and flocculating effect. 7

Preferably I maintain a concentration of the compounds of my invention in a water system of at least about 0.2 ppm. in order to prevent deposits from forming. Of course, greater concentrations may be necessary initially and for a period of time thereafter to clean a system which is already laden with deposits. Large concentrations may be added or maintained in a water system without apparent ill effect, but it is uneconomical and wasteful to maintain concentrations in excess of about 30 ppm.

A satisfactory and often more economical alternative method of practicing my invention is to periodically add to the water in the system relatively higher concentrations of the compounds of my invention for a short period of time. In this embodiment of my invention, I prefer to maintain concentrations of at least about 2 ppm. based on mass flow of water in the system, for periods usually of about 30 minutes to 2 hours, at least about once a week, although the interval between such periods of addition may range from about 4 hours to about 7 days or more. An interval should be chosen for each system which will maintain the heat exchange efficiency of the system continuously at a high level.

I have performed numerous experiments which demonstrate the effectiveness of the compounds of my invention.

In these experiments 250 ml. samples of aqueous slur- -ries containing 4 to 10% alluvial deposits obtained from various industrial cooling water systems were placed in several graduates. A different polymer was added to each graduate and the graduate was immediately inverted six times. Each graduate was closely observed to determine how rapidly the resulting floc settled to the bottom of the graduate in comparison with the floc of the other graduates. Each floc was then rated on a scale ranging from l to the number of differing settling rates obtained, 1 being a comparatively rapid settling rate, the highest number being a comparatively slow settling rate, and 2, 3, etc. being intermediate rates.

The size of the floc thereby formed was also observed and rated large, medium, or small.

Each graduate was then emptied by slow pouring and the floc observed to determine whether it flowed out easily or whether it was agglomerated. Each floc was rated on a scale beginning with 1 and ending with the number of noticeably different fluidizing characteristics observed. Thus, the most free-flowing fioc would be rated 1, the most highly agglomerated floc would have the highest rating, and other flocs would have intermediate ratings.

Control experiments were similarly conducted without the addition of a polymer.

It has been observed and determined that a superior material for alluvium control will produce a large, freeflowing floc having a rapid settling rate. Thus, in the following tables, the best materials have large floc formations, a 1 or 2 settling rate and a l or 2 fluidizing characteristic. The following tables demonstrate the consistent superiority of the material of my invention on various industrial samples compared to several standard commercial materials such as polyacrylamide.

TAB LE 1 [Deposits obtained from the heat exchange surfaces of an air compressor cooling system employing Delaware River water] Settling Fluidizing Treatment P.p.m. Floc Size Rate Characteristics Contro1- None 6 6 Polye)thylene imine (50,000-100,000 mol. 5 Large 1 1 wt. Polypropylene imine (100,000 mol. wt.) 5 do 2 2 Polyethylene imine (50,000-100,000 mol. 5 do 3 3 wt. Polyacrylamide (1-10 million mol. wt)... 5 do s 3 3 Polyethylene oxide (1-20 million mol; 5 Small 4 5 w Ethoxylated polyalkylene polyan11ne 5 do 5 4 TABLE II [Same deposits as Table I] Settling Fluidizing Treatment P.p.m. Floc Size Rate Characteristics Control 3 3 Polyethylene imine (50,000 mo 1 1 Polyethylene imine (50,000-100,000 mol. 1 1

w Polyacrylamide (1-10 million mol. wt.) 2 do 2 2 TABLE III [Same deposits as Table I] Settling Fluidizing Treatment P.p.m. Floc Size Rate Characteristics Control. None. 4 4 Polyethylene imine (100,000 mol. wt.) 1 1 Polyethylene imine (50,000100,000 mol. 2 2

w Polyethylene imine (50,000 mol. wt.) 3 3 TABLE IV [Deposits obtained from pipe lines carrying water from Lake Erie to a cooling system] Settling Fluidizing Treatment P.p.m. Floc Size Rate Characteristios Control None 5 4 Polyethylene imine (50,000-100,000 mol. 4 Large".-. 1 1

w Polyethylene imine (50,000100,000 mol. 4 do 1 2 W Polypropylene imine 4 2 3 Polyaorylamide (1 to 10 million mol. wt.) 4 3 2 Ethoxylated Polyalkylene Polyamine. 4 4 3 Polyethylene oxide (1 to 20 million mol. 4 4 3 TABLE V [Same deposits as Table IV] Settling Fluidizing Treatment P.p.m. Floo Size Rate Characteristics Control 3 3 Polyethylene imine (50,000-100,000 mol. 2 Large. 1 1 Polyethylene imine (50,000 mol. wt.) 2 Medium 2 1 Polyacrylamide (1-10 million mol. wt.) 2 do 2 2 TABLE VI [Same deposits as Table IV] Settling Fluidizing Treatment P.p.m. Floo Size Rate Characteristios Control- 4 4 Polyethylene imine (100,000 mol. wt.) 1 1 Polyethylene imine (50,000-100,000 mol, 2 2

w Polyethylene imine (50,000 mol. wt.) 2 Medium- 3 3 TABLE VII [River alluvium deposited on the heat exchange and condenser surfaces of a once through system cooling steam and air] Settling Fluidizlng Treatment P.p.m. Floc Size Rate Characterlstics Control 6 5 Polyfithylene imine (50,000-100,000 mol. 1

w 1 Polypropylene imine 2 2 Pczlvyt gthylene imine (50,000100,000 mol. 3 3 Polynerylarnide (1-10 million mol. wt.) 4 s Blend of K1 0 NaCl, starch, urea, and 5 4 polyethylene oxide (l-20 million moi. 16-10 5 4 wt.

TABLE VIII [Same deposits as Table VII] Settling Fiuidizing Treatment P.p.m. Floo Size Rate Characteristics Control None 2 2 Poiye)thylene imine (50,000100,000 moi. 2 Large 1 1 wt. Polyethylene imine (50,000 moi. wt.). 2 .do 1 1 Polyacryiamide (1-10 million mol. wt.) 2 do 1 1 TABLE IX [Deposits consisting of atmospheric dust and ailuvium from the Monongahela River deposited in an open cooling tower] [Deposits obtained from turbo blower condensers employing Monongahela River water] Settling Fluidizing Treatment P.p.m. Floe Size Rate Characteristics Control 3 5 Polyethylene imine (50,000-100,000 m 1 1 wt. Polyacrylamide (1-10 million moi. wt.) 1 2 Blend of KPO NaCi, starch, urea, and l 3 polyethylene oxide (1-20 million m l. wt.). Polyethylene imine (50,000-l00,000 moi. 2 4

TABLE XI [Same deposits as Table X] Settling Fiuldizing Treatment P.p.m Floc Size Rate Characteristics None 4 4 (1 0 mol. wt.) 2 Large 1 1 Polye)thyiene imine (150,000-100,000 moi. 2 do 2 2 wt. Polyethylene imine (50,000 mol. wt.) 2 do 3 3 In addition to these laboratory experiments, I have also conducted numerous field tests of which the following are examples:

Example I.An air cooler employing water of the Shenango River was found to be fouled with deposits of alluvium. The cooler was drained and flushed through with cooling water which removed the softer deposits.

The outlet air temperature of the cooler was 73.5 F. at this time. While the cooling water normally passes only once through the air cooler, a bypass was opened permitting water to recirculate. Then 7 p.p.m. of polypropylene imine was recirculated through the air cooler for twenty minutes. Samples of the recirculating water indicated a large amount of aluvium was removed as a floc. The cooler was again flushed with cooling water; the outlet air temperature at this time was 695 F. The bypass was again closed and 7 ppm. of polypropylene imine again recirculated through the air cooler for twenty minutes. Samples of the recirculating water indicated alluvium was still being removed. At this time the air temperature was down to 66 F. The air cooling was returned to its normal operation and forty-five minutes later the air temperature had dropped to 62.5 F. In the opinion of the observers, polypropylene imine had effected a larger decline in outlet air temperature and had removed greater quantities of alluvium than had previously used compounds. Moreover, previously it was necessary to employ air bumping in removing solids from the cooler,

a procedure which was not necessary during this trial.

Example II.--A recirculating air conditioning condenser was found to be congested with atmospheric dirt and fly ash. This caused the head pressure to rise to 210 p.s.i.g., very near the overload point of 220 p.s.i.g. Polyethylene imine of a molecular weight of 50,000 to 100,000 was maintained in the air conditioner at a concentration of 3 p.p.m., for about 24 hours. At the end of this treatment the head pressure Was reduced to 180 p.s.i.g., a normal level Operating data indicated that cleaning frequency would be reduced 50% by similar treatment whenever the head pressure reached 200 p.s.i.g.

The compounds of my invention seem to lose some of their effectiveness in waters where iron constitutes at least about 60% of the total solid content, unless at lease about 5% clay is also present, but in any event, they are still useful.

The compounds of my invention also may be used to remove mud deposits from the ballast tanks of ships and to prevent the accumulation of mud therein. If the accumulated mud is contacted under mild agitation with a solution of polyethylene imine, for example, it will form a floc which is easily flushed from the tank. By the same token,.the polyethylene imine may be fed into the ballast water inlet to form the floc before it has a chance to settle and cake. Preferably about 0.01 to 5.0 pounds of a compound of my invention should be introduced into the ballast water per ton of mud.

Thus, my invention relates to methods of preventing, controlling, and removing deposits of alluvium in cooling water systems and ballast tanks through the use of certain polyimines. I do not intend to be limited to the specific examples, compounds, and methods disclosed herein for illustrative purposes. My invention may be otherwise practiced and embodied within the scope of the following claims.

I claim:

1. The method of removing deposits of alluvium from a cooling water system comprising adding to the water of said system a polyimine having a molecular weight of at least 1000 polymerized from monomers of the general formula CEE7CHR' where R is selected from the group consisting of H and alkyl groups having up to 4 carbon atoms, and R is selected from the group consisting of R and hydroxyalkyl groups having up to 4 carbon atoms, flowing said water in contact with said deposits thereby forming a floc, and flushing said water containing said floc out of said system.

2. The method of claim 1 wherein said polyimine is polyethylene imine.

3. The method of claim 1 wherein said polyimine is polypropylene imine.

4. The method of removing and preventing deposits of alluvium in a water cooling system comprising adding to the cooling water flowing through the system a small amount of a polyimine having a molecular weight of at least 1000 polymerized from monomers of the general formula wherein R is selected from the group consisting of H and alkyl group having up to 4 carbon atoms and R is selected from the group consisting of R and a hydroxyalkyl group having up to 4 carbon atoms, said polyimine being fed for a period sufficient for the flowing water to remove an accumulation of alluvium, discontinuing said feeding for an interval during which alluvium is allowed to accumulate, and again feeding a small amount of said polyimine to said water.

5. The method of claim 4 wherein said polyimine is polypropylene imine.

6. The method of claim 4 wherein said polyimine is polyethylene imine. I

7. The method of removing alluvium and inhibiting the deposition of alluvium in a water cooling system comprising adding to the cooling water flowing through the system at least about 0.2 p.p.m. of a polyimine having a molecular weight of at least 50,000 polymerized from monomers of the general formula wherein R is selected from the group consisting of H and an alkyl group having up to 4 carbon atoms, and R is selected from the group consisting of R and a hydroxyalkyl group having up to 4 carbon atoms, said water passing through the system with sufiicient velocity to carry the treated accumulations.

8. The method of claim 7 wherein said polyimine is polypropylene imine.

9. The method of claim 7 wherein said polyimine is polyethylene imine.

10. Method of removing accumulations of mud and silt in a ballast tank comprising contacting said mud and silt with a water solution of a polyimine having a molecular weight of at least 1000 polymerized from monomers of the general formula where R is selected from the group consisting of H and an alkyl group having up to 4 carbon atoms and R is selected from the group consisting of R and a hydroxyalkyl group having up to 4 carbon atoms, whereby a floc is formed, and flushing the water containing the floc thus formed from the ballast tank.

References Cited by the Examiner UNITED STATES PATENTS 3,080,264 3/1963 Zimmie et al. 134-22 3,085,916 4/1963 Zimmie et al. 13422 3,184,336 5/1965 Murphy 13422 3,203,910 8/1965 Wilson 2602 FOREIGN PATENTS 606,968 10/ 1960 Canada. 826,770 l/1960 Great Britain.

MORRIS o. WoLK, Primary Examiner.

MICHAEL E. ROGERS, Examiner. 

1. THE METHOD OF REMOVING DEPOSITS OF ALLUVIUM FROM A COOLING WATER SYSTEM COMPRISING ADDING TO THE WATER OF SAID SYSTEM A POLYIMINE HAVING A MOLECULAR WEIGHT OF AT LEAST 1000 POLYMERIZED FROM MONOMERS OF THE GENERAL FORMULA 